Some networking applications require switching between high numbers of ports. For example, a typical data center includes a large number of servers, and switches configured to communicatively couple the servers to outside network connections, such as backbone network links. As another example, a high-volume website server system (server farm) can include a large number of web servers, and switches to communicatively couple the web servers to backbone network links. More generally, enterprise networks involve large numbers of computers communicatively coupled together via large numbers of network links, which often require switching systems that switch between large numbers of ports.
In such applications, switching systems capable of switching between a large number of ports are utilized. Such switching systems can include a large number of switches, and each switch can be capable of switching between several ports.
Some network switching systems utilize port extenders (PEs) coupled to a controlling bridge. Each PE includes a plurality of ports, and is a low complexity device that requires direction from the controlling bridge. Thus, when coupled to a port of the controlling bridge, the PE effectively increases the number of ports handled by the controlling bridge at relatively low cost.
When a packet ingresses a network switching system employing PEs, i.e., the packet ingresses a port of a source PE (a “source extended port”), the PE adds a tag to the packet, records in the tag the source extended port on which the packet was received, and then forwards the packet to the controlling bridge. The controlling bridge processes the packet (including the tag), determines a target extended port via which the packet is to be transmitted from the network switching system, and records the target extended port in the tag of the packet. The controlling bridge then forwards the packet to the target PE (which includes the target extended port). The target PE processes the tag of the packet to determine the extended port via which the packet is to be transmitted, and sends the packet to the target extended port. The target PE strips the tag from the packet prior to transmitting the packet.
The Institute for Electrical and Electronics Engineers (IEEE) 802.1BR Standard defines interactions between PEs and a controlling bridge and the content of tags utilized by PEs and the controlling bridge, as discussed above.